(1) Field of the Invention:
This invention relates to a method of enhancing the activity of a fast evaporating insecticide, and more particularly, to a method of enhancing the activity of an evaporating insecticide that rapidly evaporates the active ingredient, characterized by incorporating in a pyrethroid insecticide one or more compounds selected from the group consisting of a phthalic ester, aliphatic ester, aliphatic dibasic ester, aromatic carboxylic ester, higher aliphatic alcohol, polyhydric alcohol, glycol ether and a hydrocarbon having 10 or more carbon atoms and one or more antioxidants.
(2) Description of the Prior Art:
A fumigating insecticide is known as a conventional insecticide that evaporates the active ingredient upon short heating. Comprising an active ingredient and a combustible base that carries it, the fumigating insecticide evaporates the active ingredient using the heat of combustion produced by combustion of the combustible base. Examples of the commonly employed active ingredient are an organophosphrous insecticide, a pyrethroid insecticide, etc. The optimal temperature at which these active ingredients evaporate differs from one kind to another. However, according to this method that utilizes the heat of combustion of the combustible base, temperature control is so difficult to achieve that combustion easily results in an excessively high temperature, where as much as about 60 to 70% of the active ingredient decomposes thermally.
To eliminate such defect of the conventional method of killing insects using fast evaporating insecticides, the present inventors have conducted various studies on the effective evaporation upon short heating of a pyrethroid insecticide and its insecticidal effect, and found that by incorporating in a pyrethroid insecticide at least one compound selected from the group consisting of a phthalic ester, aliphatic ester, aliphatic dibasic ester, aromatic carboxylic ester, higher aliphatic alcohol, polyhydric alcohol, glycol ether, a hydrocarbon having 10 or more carbon atoms and an antioxidant and by evaporating the active ingredient using a heating element having an evaporating temperature suitable for the active ingredient used, a high degree of evaporation of the active ingredient can be provided and with a relatively small degree of its heat decomposition. However, we have also found that if at least one antioxidant or at least one compound other than antioxidant is independently incorporated into a pyrethroid insecticide, the degree of evaporation of the active ingredient is increased but no enhancement in the insecticidal effect is obtained.
The present inventors therefore continued their research to eliminate this defect and have finally completed the present invention which will be described hereinafter.